The invention relates to a method of locking coiled conductors in slots of a dynamoelectric machine rotor and also is concerned with particular locking members used in combination with a salient-pole rotor to lock coiled conductors in operating position around the poles of the rotor.
It is well known by those engaged in the design and manufacture of salient-poled dynamoelectric machine rotors, such as those used in synchronous generators, that it is desirable to expose as much of the energizing windings as possible directly to the air around the rotor. The reason for maximizing such exposure is to facilitate cooling of the conductors, which are otherwise thermally insulated by being tightly packed in slots defined by the respective sides of the rotor poles. It is also a necessary design consideration to assure that the coiled conductors are tightly secured in the slots with sufficient holding force to retain them in their optimum operating positions against the centrifugal force that is exerted on the conductors when the rotor is placed in operation. In the past, two primary techniques were used to secure such coiled conductors in their slots. For relatively small diameter rotors, a coarse tape, or roving, was wound around and between the coiled conductors and securely tied to hold them in place in the rotor slots. For larger rotors, that frequently develop greater centrifugal forces on the rotor conductors, the usual practice was to provide two or more insulated studs threaded into the center of each rotor slot prior to winding the conductors in the slots. After such winding was completed, an insulated metal clip was fastened down against the coiled conductors by mounting the clip over the conductors and forcing it toward them by tightening threaded nuts on the studs mounted in the slots.
Such prior art technology, while effective to afford the desired objective of securing the rotor conductors in operating position, did involve certain disadvantages. The use of roving tied to coiled rotor conductors to secure them in operating position is a relatively expensive process due to the level of skill required to effectively employ it. Moreover, even a skilled assembler requires considerable time to properly tie a rotor winding in operating position with this technique. The primary disadvantages of using threaded studs to secure rotor windings in operating position is that such assemblies are relatively costly and the studs protrude from the winding slots thus interfering with an assembler engaged in winding magnet wire in the slots.
In addition of the two foregoing techniques that are usually employed in manufacturing rotors having random wound windings, other conductor securing techniques and locking means are known. For example, U.S. Pat. No. 2,745,030 discloses a U-shaped wedge that is mounted over a form wound coil of a rotor then swedged into recesses provided in the rotor above the form wound conductors in order to lock the conductors in the winding slots of the rotor. U.S. Pat. No. 1,564,449 describes the use of a resilient clip that is pressed into a rotor slot in a deformed condition and then allowed to straighten so that the ends of the clip extend, respectively, under the tips of poles forming the periphery of the rotor. In their expanded positions, the resilient clips operate to hold conductors in operating position in winding slots that are located directly beneath the clips on the rotor. A somewhat related resilient conductor retaining means is also shown in U.S. Pat. No, 1,891,200. As explained in that patent, a retaining means in the form of a deformable insulating material, such as rope, is pressed against the upper surface of a plurality of coiled conductors positioned in a winding slot of a rotor in order to drive the retaining means into the slots and cause it to expand underneath adjacent tips of salient poles that form the walls of the slots. In its expanded position the rope, or other expandable retaining means, is effective to retain the coiled conductors in the slots.
A common disadvantage of the three conductor retaining means described by the three patents just identified is that they completely cover the axial length of the conductors disposed between the ends of the winding-receiving slots. Thus, the windings cannot be optimumly cooled in the normally desired manner noted above.
Another type of relatively common rotor construction that is somewhat related to the present invention is one that uses insulating slot covers that inherently have some coil-locking benefit. Examples of such conventional slot wedges are shown in U.S. Pat. Nos. 2,283,146; 3,335,610 and 3,519,862. As explained in the first two of these patents, it is common to use such conventional insulating slot wedges to perform additional functions, such as to limit the movement of carbon dust relative to the winding slots. Also, as indicated in the third patent just mentioned, such slot wedges often are used to provide a separation between multiple phase windings mounted in the same slots of a rotor. A common characteristic of such slot wedges, which is a disadvantage in terms of conductor cooling, is that they typically extend over the entire axial length of the conductors wound in the rotor slots. Thus, the outer surface of the coiled conductors is not exposed to the ambient for cooling, in the desirable manner described above.